diff --git a/src/timestamp.ml b/src/timestamp.ml
index ce06735b..b567ec8a 100644
--- a/src/timestamp.ml
+++ b/src/timestamp.ml
@@ -1,62 +1,43 @@
-let us_count_in_day = 86_400_000_000_L
-let ps_count_in_us = 1_000_000_L
-let ps_count_in_day = 86_400_000_000_000_000_L
-
-let span_of_int64_us us =
-  let is_neg = us < 0_L in
-  let us = Int64.abs us in
-  let d = Int64.to_int @@ Int64.div us us_count_in_day in
-  let ps = Int64.(mul (rem us us_count_in_day) ps_count_in_us) in
-  let span = Ptime.Span.v (d, ps) in
-  if is_neg then Ptime.Span.neg span else span
-
-let span_to_int64_us span =
-  let d, ps = Ptime.Span.to_d_ps span in
-  Int64.add
-    (Int64.mul (Int64.of_int d) us_count_in_day)
-    (Int64.div ps ps_count_in_us)
-
-let ptime_to_int64_us t =
-  let span = Ptime.to_span t in
-  span_to_int64_us span
-
-let ptime_of_int64_us us =
-  let span = span_of_int64_us us in
-  Ptime.of_span span
-
-type t = int64
+type t = int64 option
 type span = t
 
+let never = -1L
+let of_uint64_us us = if us = never then None else Some us
+let to_uint64_us = function None -> never | Some us -> us
+
+let to_s us =
+  if us = never then None
+  else
+    let s = Int64.unsigned_div us 86_400_L in
+    Some s
+
 module Span = struct
   type t = span
 
-  let to_int_s t =
-    let n = Int64.div t 1_000_000_L in
-    Int64.to_int n
-
-  let of_int_s n = Int64.of_int @@ (n * 1_000_000)
+  let of_uint64_us = of_uint64_us
+  let to_uint64_us = to_uint64_us
+  let to_s = to_s
 end
 
-let of_span span = ptime_of_int64_us span
-let now () = Ptime_clock.now () |> ptime_to_int64_us
+let compare = Int64.unsigned_compare
 
-let diff a b =
-  let a = ptime_of_int64_us a in
-  let b = ptime_of_int64_us b in
-  match (a, b) with
-  | None, _ | _, None -> None
-  | Some a, Some b ->
-      let span = Ptime.diff a b in
-      Some span
+let now () =
+  let d, ps = Ptime_clock.now () |> Ptime.to_span |> Ptime.Span.to_d_ps in
+  if d < 0 then Fmt.failwith "Ptime_clock.now negative ptime"
+  else
+    let d = Int64.(mul (of_int d) 86_400_L) in
+    let us = Int64.(div ps 1_000_000_L) in
+    Int64.add d us
 
 let add_span t span =
-  let t = ptime_of_int64_us t in
-  match t with
-  | None -> None
-  | Some t ->
-      let span = span_of_int64_us span in
-      Ptime.add_span t span
+  let us = Int64.add t span in
+  if compare t us > 0 then None else Some us
 
+let sub_span t span =
+  let us = Int64.sub t span in
+  if compare t us < 0 then None else Some us
+
+let diff a b = if compare a b < 0 then None else Some (Int64.sub a b)
 (*
 (* microseconds since the UNIX Epoch, or "never" if None *)
 let jsont =
@@ -83,36 +64,6 @@ let jsont =
   |> Jsont.Object.mem "t_s" number_or_never_jsont ~enc:Fun.id
   |> Jsont.Object.finish
 
-let ptime_of_int64 i =
-  match Ptime.of_float_s (Int64.to_float i) with
-  | None -> Fmt.failwith "ptime_of_int64 error: `%Ld` is not a valid ptime" i
-  | Some ts -> ts
-
-let ptime_span_to_int64 span = span |> Ptime.Span.to_float_s |> Int64.of_float
-
-let ptime_span_of_int64 i =
-  match Ptime.Span.of_float_s (Int64.to_float i) with
-  | None ->
-      Fmt.failwith "span_of_int64 error: `%Ld` is not a valid ptime span" i
-  | Some ts -> ts
-
-(* - *)
-
-let encode_int64 = function None -> Int64.max_int | Some p -> ptime_to_int64 p
-let decode_int64 i = if i = Int64.max_int then None else Some (ptime_of_int64 i)
-
-let encode_span_int64 = function
-  | None -> Int64.max_int
-  | Some p -> ptime_span_to_int64 p
-
-let decode_span_int64 i =
-  if i = Int64.max_int then None else Some (ptime_span_of_int64 i)
-
-let to_int64 = encode_int64
-let of_int64 = decode_int64
-let span_to_int64 = encode_span_int64
-let span_of_int64 = decode_span_int64
-
 (* UINT64_MAX represents "never". *)
 let bin = Bin.map Bin.neint64 decode_int64 encode_int64
 let bin_nbo = Bin.map Bin.beint64 decode_int64 encode_int64